The embodiments described herein relate generally to electrical machines, and more particularly, to methods and systems for cryocooling of electrical machines.
Some electrical machines, such as generators or motors, can have a rotating rotor and a stationary stator. The use of superconducting windings in some electrical machines can result in an increase in electromagnetic forces generated by the windings and an increase in flux densities within the machines. The current density and thus the specific power of these machines can be increased, and the efficiency of the machine can also be increased by the use of cryocoolers. Cryogenically cooled windings of electrical machines, however, typically have to be thermally isolated from the environment and have to be kept at a required low temperature by a coolant. Effective thermal isolation can be achieved for the cryogenically cooled parts by separating the cooled parts from warmer components of the electrical machine.
Conventional superconducting generators may include high power, forced-flow cooling systems. Forced-flow cooling systems, however, may include bulky, large and costly equipment such as, for example, helium pumps, blowers and/or helium refrigeration systems. Besides sometimes being unwieldy and fault-prone, these components may not fit within operational housings such as, for example, nacelles of wind turbines.
Moreover, some conventional superconducting generators may include torque transfer assemblies that can absorb and/or transfer torque generated by electromagnetic loads of components such as stators and/or rotors. Conventional torque transfer assemblies, however, may include large torque tubes which can increase the required space footprint within operational housings. Moreover, some conventional torque tubes are inefficiently coupled to heat loads which may lead to inadvertent heat transfer losses.
Furthermore, some conventional superconducting generators may include a coil former that includes coil windings positioned on an outer surface of the coil former. A lid may be needed to couple the coil winding to the coil former to resist electromagnetic radial forces applied to the coil windings. Lids, however, may necessitate increasing the required air gap between rotating and stationary components which could add to increased space requirements and cost to the superconducting generator. Moreover, conventional lids may decrease the heat transfer from the coil windings.